# Ideal Gas Law Calculator (PV = nRT)

Calculate pressure, volume, temperature, or moles using the ideal gas law PV = nRT. Solve for any variable. Free online thermodynamics calculator.

## What this calculates

The ideal gas law PV = nRT is one of the most important equations in chemistry and physics. It relates pressure (P), volume (V), amount of substance (n), and temperature (T) through the universal gas constant R = 8.314 J/(mol·K). This calculator solves for any one variable given the other three.

## Inputs

- **Pressure (P)** (Pa) — min 0 — Standard atmospheric pressure: 101,325 Pa
- **Volume (V)** (m³) — min 0
- **Amount of Substance (n)** (mol) — min 0
- **Temperature** (K) — min 0 — Must be in Kelvin (K = °C + 273.15)
- **Solve For** — options: Pressure, Volume, Moles, Temperature

## Outputs

- **Calculated Value** — The solved variable from PV = nRT
- **Unit** — formatted as text — Unit of the calculated value
- **Pressure** (atm) — Pressure in atmospheres
- **Temperature** (°C) — Temperature in Celsius

## Frequently Asked Questions

**Q: What is the ideal gas law?**

A: The ideal gas law PV = nRT describes the behavior of an ideal gas, where P is pressure (Pa), V is volume (m³), n is the number of moles, R is the universal gas constant (8.314 J/mol·K), and T is temperature in Kelvin. It combines Boyle's, Charles's, and Avogadro's laws into a single equation.

**Q: When does the ideal gas law break down?**

A: The ideal gas law assumes no intermolecular forces and negligible molecular volume. It breaks down at very high pressures (molecules forced close together), very low temperatures (intermolecular forces become significant), and near the condensation point. For these conditions, the Van der Waals equation or other real gas equations provide better accuracy.

**Q: Why must temperature be in Kelvin?**

A: The ideal gas law requires absolute temperature because pressure and volume are proportional to absolute temperature. At 0 K (absolute zero), an ideal gas would have zero volume and zero pressure. Using Celsius would give negative temperatures that produce nonsensical negative volumes or pressures. Convert by adding 273.15: K = °C + 273.15.

**Q: What is the universal gas constant?**

A: The universal gas constant R = 8.314462 J/(mol·K) relates energy to temperature on a per-mole basis. It equals the product of Boltzmann's constant (k_B) and Avogadro's number (N_A). R appears in many thermodynamic equations beyond the ideal gas law, including entropy calculations and chemical equilibrium expressions.

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Source: https://vastcalc.com/calculators/physics/ideal-gas-law
Category: Physics
Last updated: 2026-04-21